The present invention relates to a semiconductor laser element required for optical information processing such as in an optical fiber communication system, an optical measurement system, or an optical disk system, and a method of producing the same. In particular, the present invention relates to a semiconductor laser element suitable for producing a semiconductor laser device having a plurality of laser chips packaged together.
Semiconductor laser devices are used for optical communications, optical measurement systems, optical disc systems and the like. In particular, the market in the field of optical discs has been remarkably expanding and various kinds of optical discs, such as CD, MD, DVD, have come to be used for data preservation for computers and the like. These circumstances require semiconductor lasers having oscillation wavelengths in various wavelength regions including an infrared region, red region and further a blue region in future.
In order to record/reproduce signals to/from various kinds of optical discs using only one optical disc system, it is required that a semiconductor device having various kinds of oscillation wavelengths be packaged in the optical disc system. A semiconductor laser device is constructed by mounting a semiconductor laser element on a mount called stem and packaging it in one container. In order to realize a semiconductor laser device that achieves various kinds of oscillation wavelengths, it is required to use a so-called monolithic type semiconductor laser device wherein a semiconductor laser element having two or more laser resonators is mounted on a stem, or to use a so-called hybrid type semiconductor laser device in which two or more semiconductor laser elements are mounted close to each other on a stem.
FIG. 7 is a view explaining a conventional semiconductor laser device. In the shown semiconductor laser device 70, a semiconductor laser element 73 is mounted on a heat dissipation plate 72, which is integrated with a stem 71. The semiconductor laser element 73 and a monitoring photodetector 74 are connected to lead pins 78, 78 by metal wires 77, 77, respectively, the lead pins 78, 78 being electrically insulated from each other. Another lead pin 78 is connected to the stem 71, which pin is used as a common terminal of the semiconductor laser element 73 and the monitoring photodetector 74.
In order to protect the semiconductor laser element 73, the metal wires 77 and the like from mechanical impact and the like, a metal cap 75 provided with a glass window 76 that transmits laser beams is welded to the stem 71.
FIG. 8 is a view of a main part of a hybrid-type semiconductor laser device seen from a laser beam emitting side of the device. This device is the same as the semiconductor laser device 70 of FIG. 7, except that two semiconductor laser elements 80, 81 are juxtaposed or disposed in parallel on a heat dissipation plate 82, and that these elements are individually connected to different lead pins (not shown) through metal wires (not shown).
The hybrid-type semiconductor laser device is characterized in that different semiconductor laser elements are freely combined. Generally, in the individual optical disc systems, an optical system is constructed on the basis of optical axes of laser beams. Therefore, the distance between adjacent optical axes should preferably be short, and moreover the distance between the adjacent optical axes should preferably be constant in the individual semiconductor laser devices. That is, in the case of the semiconductor laser device shown in FIG. 8 in which optical axes of the semiconductor laser elements 80, 81 are substantially parallel to waveguides (not shown) which pass through light emitting points 80a, 81a of the semiconductor laser elements and extend in a direction perpendicular to the surface of the drawing sheet, it is required that the distance dx between the light emitting points 80a, 81a be short and not changed among different semiconductor laser devices.
If the distance dx between optical axes is long, when an optical system is constructed such that a signal from one type of optical disc can be, detected, signals from other types of optical discs may not be detected. Further, when the distance between the optical axes is changed among the semiconductor laser devices, without a design change of the optical system or a substantial assembling adjustment made on the individual semiconductor laser devices, the following problems may occur: laser beams cannot be condensed accurately on an optical disc, signals cannot be read out, and so on. Thus, it becomes practically impossible to use such an optical system.
In order to shorten the distance dx between the adjacent light emitting points in the hybrid-type semiconductor laser device, for example, as shown in FIG. 8, it is required that the light emitting point 80a, 81a of each semiconductor laser element be positioned nearer to one side face of the semiconductor element than to the other side face. The reason thereof is as follows. The semiconductor laser element usually has a dimension in the range of 200 xcexcm-300 xcexcm in its widthwise or lateral direction i.e. a direction which is perpendicular to an extending waveguide of the semiconductor laser element and is parallel to a die bonding face 82a, while the distance dx between the light-emitting points of two semiconductor elements is required to be not more than 100 xcexcm with an accuracy of about xc2x110 xcexcm. Therefore, it is required that the distances from the light emitting points 80a, 81a to the respective side faces of the elements be not more than 50 xcexcm. On the other hand, when the distance from the particular side face of the light emitting point of the semiconductor laser element is too short, for example 5 xcexcm or less, there is a problem that its properties are deteriorated. For this reason, the position of the light emitting point must be arranged so as to be 5-50 xcexcm distance from the side face.
Furthermore, in the hybrid-type semiconductor laser device, the light emitting points of the semiconductor laser elements are not centered. Thus, if an element is mounted in a wrong direction on the stem, the other element cannot be mounted, which is a problem. For example, if the semiconductor laser element 81 is wrongly oriented when mounted on the heat dissipation plate 82 based on the position of the light emitting point 80a of the other semiconductor laser element 80 on the heat dissipation plate 82, the opposed side faces of the semiconductor laser elements 80, 81 will bump against each other. Thus, the semiconductor laser element 81 cannot be mounted.
The present invention has been made with a view to solving the above problems, and an object of the present invention is to provide a semiconductor laser element having a light-emitting point positioned relative to a particular side face with high accuracy and free from mounting in a wrong direction such that use of the elements realizes a good hybrid-type semiconductor laser device, and also to provide a method of producing such a semiconductor laser element.
In order to accomplish the above object, the present invention provides a semiconductor laser element comprising a semiconductor substrate and a crystalline layer formed on a main surface of the semiconductor substrate, the crystalline layer having in its inside a waveguide, wherein the semiconductor laser element further comprises:
a light-emitting point alignment mark provided on an intersection line of an electrode surface of the semiconductor laser element with a plane which includes the waveguide and which is perpendicular to the electrode surface;
said light-emitting point alignment mark having a length in a width direction of the semiconductor laser element of not more than 20 xcexcm; and
a visually recognizable direction indicating mark.
With the above arrangement, in producing a hybrid-type semiconductor laser device using the semiconductor laser element of the present invention, it is possible to narrow the distance between two light emitting points of the semiconductor elements, without causing the opposed side faces of the semiconductor laser elements to bump against each other thanks to the direction indicating mark. Also, because the lateral positions (namely, positions in the width direction of the element) of the light emitting point and the light-emitting point alignment mark coincide with each other with a predetermined accuracy, it is possible to improve the accuracy of the distance between the side face and the light emitting point of the semiconductor laser element.
In order to facilitate the correct mounting of the semiconductor laser element, the direction indicating mark may be provided on the same side as the light-emitting point alignment mark in a direction in which the waveguide extends.
In one embodiment, the direction indicating mark consists of a polygon whose shortest side is longer than 20 xcexcm or an ellipse whose minor axis is longer than 20 xcexcm.
By this arrangement, it is possible to visually check the orientation of the semiconductor laser element, so that misorientation of the semiconductor laser element is avoided. This makes it possible to improve the productivity of semiconductor laser devices using the laser elements of the present invention.
The semiconductor laser element may further include a side alignment mark and an additional mark projecting laterally outwards of the side alignment mark. The additional mark may have a stepped shape such that the additional mark has various portions that are at different distances from a side face of the semiconductor laser element.
By this arrangement, the accuracy of the distance from the side face to the light emitting point of the semiconductor laser element can easily be evaluated, thus making it possible to improve the productivity more.
The present invention also provides a method of producing a semiconductor laser element comprising the steps of:
placing a photomask on a wafer, said photomask formed with a plurality of semiconductor laser element patterns each having a light-emitting point alignment mark and a side alignment mark;
adjusting widthwise distances between the light-emitting point alignment marks of the photomask and respective light emitting points in the wafer such that the distance falls within a predetermined range;
forming a plurality of semiconductor laser element patterns on the wafer using the photomask;
dividing the wafer into individual semiconductor laser elements; and
judging whether each of the divided semiconductor laser elements is defective or non-defective by observing whether or not there is a missing part in the side alignment mark on the semiconductor laser elements.
This method can produce semiconductor laser elements having respective light-emitting points positioned at a required distance from pertinent side faces with accuracy. Also, with this method, defectives are easily found if any. Thus, it is possible to improve the productivity of the semiconductor laser elements.
In one embodiment, the step of adjusting widthwise distances between the light-emitting point alignment marks of the photomask and respective light emitting points in the wafer includes observing widthwise distances between the light-emitting point alignment marks of the photomask and respective waveguides in the wafer for the semiconductor laser elements to be produced.
Such an observation makes it possible to improve the accuracy of the distance between the light emitting point and the side face more.
The observation may be performed using an infrared microscope. The observation using an infrared microscope is convenient especially when an off-orientation wafer is used.
In one embodiment, the predetermined range for the widthwise distances between the light-emitting point alignment marks and the light-emitting points is from xe2x88x9210 xcexcm to +10 xcexcm.
In one embodiment, the plurality of semiconductor laser element patterns of the wafer are formed by etching a top layer of a multi-layered electrode layer of the wafer.
In one embodiment, each semiconductor laser element pattern of the photomask has an additional mark projecting laterally outwards of the side alignment mark in a stepped manner. In this case, each semiconductor laser element pattern of the wafer has an additional mark projecting laterally outwards of the side alignment mark in a stepped manner. Due to the additional mark projecting like steps or stairs, which can serve as a scale, it is possible to adequately adjust the position of a marking-off line for dividing the wafer.
Other objects, features and advantages of the present invention will be obvious from the following description.